Effects of oxygen nonstoichiometry on the stability of antiferromagnetic phases of CuFeO2+δ single crystals

Effects of oxygen nonstoichiometry on stabilities of the antiferromagnetic (AF) phases of CuFeO2 with a delafossite-type structure have been investigated. Temperature dependence of the magnetic susceptibility between 5 and 300 K in 0.1 T parallel to the c axis, and magnetic-field dependence of the magnetization below 40 T parallel to the c axis at 4.2 K are clarified using CuFeO2 + delta single crystals with stoichiometry varying from oxygen deficiency (delta = -0.026, -0.061) to oxygen excess (delta = 0.14, 0.085). It is found that the stabilities are strongly affected by the oxygen defects, depending on their type, i.e., oxygen deficiency or oxygen excess. The transition temperature between the four-sublattice AF phase (low-temperature AF phase) and the partially disordered phase (high-temperature AF phase) is increased by the oxygen deficiency, whereas it is decreased by the excess oxygen. It should be noted that both types of oxygen defects bring another metamagnetic transition around 23 T. Besides, all metamagnetic transition fields are increased by the oxygen defects. These effects are discussed from the viewpoints of crystal chemistry.